You are looking at the HTML representation of the XML format.
HTML is good for debugging, but is unsuitable for application use.
Specify the format parameter to change the output format.
To see the non HTML representation of the XML format, set format=xml.
See the complete documentation, or API help for more information.
<?xml version="1.0"?>
    <alltransclusions gatcontinue="Provenance" />
      <page pageid="45" ns="10" title="Template:External Reference Repeater" />
      <page pageid="46" ns="10" title="Template:External References" />
      <page pageid="6464" ns="10" title="Template:Gene Ontology Reference Repeater" />
      <page pageid="47" ns="10" title="Template:Gene Synonym Repeater" />
      <page pageid="48" ns="10" title="Template:Gene Synonyms" />
      <page pageid="50" ns="10" title="Template:Ontological References" />
      <page pageid="63279" ns="10" title="Template:Ontology Result Format" />
      <page pageid="63281" ns="10" title="Template:Ontology Result Format Footer" />
      <page pageid="63280" ns="10" title="Template:Ontology Result Format Header" />
      <page pageid="51" ns="10" title="Template:Plant Ontology Reference Repeater" />